Dopamine-beta-hydroxylase (EC 1.14.17.1; DBH) is the biosynthetic enzyme which catalyzes the conversion of dopamine to norepinephrine in sympathoadrenal cells and CNS neurons. During the exocytotic release of norepinephrine, DBH protein is released along with the neurotransmitter. This released DBH protein can be measured in both the circulatory pool and the cerebrospinal fluid. We have assayed CSF DBH levels in non-medicated Parkinson's disease patients, and found a significant decrease in their DBH levels to 41% control. This finding suggests that alterations and/or deficits central noradrenergic function are occurring in Parkinson's disease.